A Study of Charge-Transfer Reactions on (110) Single-Crystal Nickel Surfaces in Nickel Sulfamate Electrolyte Using Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy measurements under a small alternating current density were performed to investigate electrochemical reactions on (110) single-crystalline nickel surfaces in nickel sulfamate electrolyte. The reaction impedance shows a power law of the ac modulation frequency, and two exponents for the reaction resistance and reaction capacitance are found to approximately agree with the values predicted by a homogeneous charge-transfer reaction model. In addition, the Nyquist diagrams exhibit the absence of inductive loops for the frequency range from 50 mHz to 100 kHz. A condition for the existence of inductive loops derived in this study suggests that the electrocrystallization of Ni 2+ ions may take place in the slow reaction step Ni 2+ + e - → and in the fast reaction step + e - → Ni.